Tesco was said to have triggered aggressive responses from rivals with its 'big price drop' campaign launched in September Photograph: imagebroker / Alamy/Alamy

The latest inflation figures expose the impact of the price war in the supermarkets. Darren Shirley, an analyst at City broker Shore Capital, suggested Tesco's "big price drop", its £500m price cut campaign launched at the end of September, was the trigger for aggressive responses from rivals.

The big four – Tesco, Asda, Sainsbury's and Morrisons – ring up three-quarters of the UK's annual £150bn grocery bill and are fighting for market share as sales volumes decline for the first time in more than a decade. Britons are sticking to their shopping lists.

Morrisons chief executive Dalton Philips said consumers were "feeling bruised" and predicted a third of its shoppers would dip into savings to cover the cost of Christmas. The retailer said it was dishing out £100m of savings over the festive period, focused on "sharp, single item prices" as shoppers did not want to have to spend more on multibuy offers. Although food prices fell 0.9% in October the headline food inflation figure remains 5% and Philips cautioned against assuming the worst was over: "Until we can see what's going to happen in oil it's too hard to call."

IGD chief economist James Walton said most foods, except fish, had become "slightly cheaper" in recent weeks but the grocers should not take all the credit. "Much of this may be due to price falls on global markets."

The unprecedented pressure on household incomes has given rise to a breed of "professional" shopper who goes from store to store to secure the best deals – even venturing to discounters Aldi and Lidl, which are reporting bumper sales numbers not seen since the depths of the recession.

With the surge in the price of petrol more shoppers are using convenience stores to avoid driving. Asda reported a "solid" 1.3% rise in like-for-like sales for the third quarter although fewer shoppers visited its stores, instead consolidating their trips in the fact of high fuel prices, the company said.

Sainsbury's chief executive Justin King said inflation in shopping trolleys was far lower than official figures suggested. He said shoppers "dial it out" by buying cheaper own-label products, using vouchers and buying only when goods are discounted. Zoe Wood